Ferrofluid seal apparatuses are known for sealing rotary shaft elements, such as for use as an exclusion-type seal or as a pressure capacity-type seal. Such ferrofluid seal apparatus provides an effective seal between different environments, either at the same or at different pressure, or having the same or different environments.
A ferrofluid exclusion-type single stage, single pole piece seal apparatus is described in U.S. Pat. No. 4,407,508, Issued Oct. 4, 1983, wherein a single pole piece and a single annular permanent magnet are employed to provide a single stage exclusion-type seal wherein the magnetic flux circuit is completed through an air gap between one end of the permanent magnet and the shaft element to be sealed. A multiple stage pressure capacity-type ferrofluid seal apparatus is described, for example, in U.S. Pat. No. 3,620,584, Issued Nov. 16, 1971, which patent describes a multiple-stage ferrofluid seal apparatus employing an annular permanent magnet and a plurality of separate spaced apart ferrofluid O-ring seals extending about the surface of the shaft element to be sealed, each seal providing its own defined pressure capacity and employing two pole pieces, one on either side of the annular permanent magnet. In addition, magnetic bearing systems, such as a ball bearing, have been used to support a rotary shaft and to permit the low friction rotation thereof and employed ferrolubricants retained within the confines of the inner and outer race of the ball bearing assembly, such as, for example, described in U.S. Pat. No. 3,977,739, Issued Aug. 31, 1976.
It is desirable to provide a pressure capacity-type ferrofluid seal apparatus which is more compact than conventional, multiple-stage ferrofluid seal apparatus, and which seal apparatus may be constructed at lower cost with the use of lower magnetic power consumption and yet have the same or substantially the same pressure capacity, as required in the prior art ferrofluid seal apparatus.